Nerves crept in as he attempted to serve out the match, but del Potro converted his fourth match point opportunity after two hours and 22 minutes, having hit 36 winners and broken Seppi twice.

“I played really well, but in the end I was so nervous I couldn’t close the match out easily,” admitted del Potro. “In the third set, I missed easy forehands because of nerves. I think I played really well the last two points of the match."

Two days earlier, Del Potro had injured his knee in a fall towards the end of his third-round victory over Grega Zemlja and was coy when asked about his fitness.

"My knee is almost fine. Two days ago, I twisted my ankle and hyperextended my knee, but I've been icing it and relaxing and the doctors are helping me to recover,” the Argentine told BBC immediately after the match, but later revealed in his press conference that he is in a certain amount of discomfort.

“The ankle is good and the knee is not good. But I'm allowed to play. It still bothers me in the left outside of the knee. But the doctor says it’s nothing too dangerous, and that's positive.

“I couldn't extend the knee 100 per cent. And the tapes for today helped me to be careful in some movements. But it is not enough. I have one day and a half until my next match, and I will do all the treatments to see if I can be better.”

For a place in the semi-finals, del Potro will look to overturn a 2-6 record against fourth seed David Ferrer in their FedExATP Head2Head series, which includes a defeat to the Spaniard in the Round of 16 last year at the All England Club. Ferrer has won four straight meetings overall, most recently in the round robin stage of the 2012 Barclays ATP World Tour Finals.

“I’m so happy to be in the quarter-finals for the first time here in Wimbledon. I’m improving playing on grass; I like it a lot," del Potro said. “It’s going to be difficult against Ferrer, but I’m very excited to play him. He's playing fantastic this season; he will be No. 3 in the world. I think he's the favourite, but I like to play this match on the grass. If my knee is OK, I think it will be a good match.”

The 24-year-old del Potro came into Wimbledon after a quarter-final showing at The Queen’s Club (l. to Hewitt), having missed Roland Garros and the climax to the clay-court season due to a respiratory illness. He is bidding to reach his first major semi-final since winning his first Grand Slam championship at the 2009 US Open, beating Rafael Nadal and Roger Federer back-to-back.